It is known to use low dosage X-rays so as to provide latent images which may be stimulated off-line so as to expose the hidden images. Such a technique is disclosed, for example in U.S. Pat. No. 4,547,670. As disclosed in EP 423 891 the latent images are produced by X-rays which impinge on a specially coated film containing a suitably reactive material. The latent image is stored in the coating as a spatially distributed pattern of excited electrons which are trapped in a manner quantitatively indicative of an amount of electromagnetic energy spatially distributed on the film. A visible image can be derived from the resultant latent image by inducing the trapped electrons to fluoresce such that the intensity of the fluorescence is quantitatively indicative of the intensity of the spatially distributed X-ray radiation which was originally absorbed by the film. After the information has been extracted, the entire film is exposed to light, thereby leveling off all of the X-ray excitable electrons to a non-energized state, thus conditioning the film for re-use.
Image scanners have become very common for converting many types of analog input data into computer compatible information. Such scanners have a laser light source for directing on to a film which is generally disposed on a surface of a drum, and are further equipped with means for reading the light reflected by the film.
FIG. 1 shows such a radiographic latent image reader for exposing a phosphor storage sheet to an excitation laser beam as described in JP 6019014. A laser beam 30 from a laser light source 16 is reflected by mirrors 22 and 24, passes through a selecting mirror 26 and a condensing lens 28, and irradiates the recording surface 12 of a stimulatable phosphor 10. The fluorescence generating by the phosphor 10 is condensed by the lens 28, reflected by the mirror 26 and detected by a fluorescence detecting device 20 after its red light reflections are cut by a filter 34. By subjecting the reader to transverse motion in the direction shown by the arrow 15 so as completely traverse the width of the recording surface 12, the entire surface of the phosphor 10 may be read.
It is apparent, therefore, that in the system described in JP 6019014, complex imaging and scanning optics are required which are cumbersome and space-consuming. This, in turn, militates against the provision of more than one scanning optics per drum so as to scan along only a fraction of thereof, thereby allowing different sections of the film to be scanned by more than one scanning optics simultaneously. As a result, such prior art systems are relatively slow.
It would obviously be desirable to replace the complex imaging and scanning optics of JP 6019014 with a compact unit allowing several such units to be provided along the width of the film, so as to allow parallel processing thereof. The prior art makes no attempt to address this requirement.
U.S. Pat. No. 4,302,671 (Kato et al.) discloses a radiation image readout device for reading a stimulatable phosphor. The radiation image readout device includes a photosensor for detecting light produced by the phosphor upon its being stimulated, and a reflecting optical element like a mirror located between the phosphor and the photosensor for reflecting stimulating rays advancing between the phosphor and the photosensor towards the phosphor. The reflecting optical element has a very small size not to intercept the light emitted by the phosphor and detected by the photosensor as much as possible.
The stimulatable phosphor is mounted on a rotary drum and the photosensor is secured to a readout head which is movable in the direction of the axis of the drum. Stimulation of the phosphor is achieved by means of a laser mounted parallel to the drum's axis so as to direct a beam of laser light between the photosensor and the drum so as to be reflected by the mirror toward the stimulatable phosphor plate.
Such an arrangement is also not adapted for multiple reading heads since the stimulating laser beam is directed towards the photosensor along the axis of the drum. Consequently, at most two reading heads might possibly be employed in back-to-back arrangement with respective laser beams directed in opposite directions towards each other. There is no obvious way to employ such an arrangement for the simultaneous stimulation and reading of more than two points on the phosphor. Furthermore the arrangement lacks compactness, is relatively slow and expensive.